The growing concern over the health of the baby born
to a mother with variant CJD and the new evidence, announced last week,
that the disease may have spread through blood transfusions, highlight
the disturbing ability of vCJD to surprise the experts.

A conclusive diagnosis of vCJD in the 11-month-old child
would imply a far shorter incubation period than many scientists thought
possible. It would also mean that the disease can be passed down the generations,
not merely acquired through contact with infected tissue.

Scientists have yet to pin down the likely size of the
vCJD epidemic, with estimates for Britain ranging from about 100 cases
to more than 100,000; so far there have been only 82 probable or confirmed
cases. The case of the baby girl means that scientists are now admitting
that many predictions may have to be rethought.

According to Dr Neil Ferguson of the University of Oxford,
a leading expert on the mathematics of epidemics, so-called vertical transmission
down the generations has, at least until now, been thought to be relatively
unimportant.

Dr Ferguson said: "It very much depends on the probability
of it taking place. If a woman has to be very sick and symptomatic in order
to give it to her baby, then the number of cases it creates are going to
be very small, because she is unlikely to get pregnant."

The mother of the baby at the centre of the current concern
is, however, understood to have been showing only minor symptoms of the
disease at the time of conception; only later in her pregnancy did she
develop the classic symptoms of vCJD from which she died in May this year.

Richard Lacey, an emeritus professor of medical microbiology
at Leeds University, said that the Telegraph story had wider implications
than its obvious medical significance. Prof Lacey said: "The only
thing that is certain is the scale on which it is happening. That will
take decades to find out. I am aware of other cases where maternal transmission
could be an issue; this isn't the only one.

"This poses difficult ethical problems: to what
extent should individuals be told of the risk? Should such a person be
told not to give blood when he or she is old enough to do so? What effect
will this knowledge have on that person's way of life, on their emotions?
There needs to be some sort of discussion about how we cope with it, but
at the moment there is nothing."

Epidemiologists are puzzled by the fact that vCJD is
predominantly affecting young people, while classic CJD is a disease of
the old. Prof Lacey suggested that one possible explanation is that the
teenagers and young people who have died from vCJD may have contracted
the disease from their mothers while in the womb. He added that it is a
recognised clinical syndrome that infectivity accumulates when it is passed
on from one generation to the next.

Dr Stephen Dealler, an expert on BSE and vCJD at Burnley
Hospital, said that it had been believed that mother-to-offspring infection
could take place in cows, but only with a considerable incubation period.
"The thinking is that it may take place in cows, but the incubation
period is still three to five years," he said. "This would lead
us to expect an incubation period of around seven years in humans. If the
baby does have vCJD, that's a very fast incubation period."

Last week's revelation resulting from animal experiments
that the disease may be transferred through blood transfusions from infected
people with no symptoms was being played down by government scientists,
who said that all British blood is screened to remove cells that may harbour
vCJD.

The Telegraph has learnt, however, that the Department
of Health is seriously considering the use of disposable surgical instruments
throughout the National Health Service. This follows growing concern that
blood and tissue from asymptomatic carriers of the disease could remain
infectious even after sterilisations.